Circuits for splitting or joining radio-frequency power are known, for example, as so-called bridge circuits or as Wilkinson couplers and are used in particular for connecting radio-frequency transmitters or antennas in parallel, in radio-frequency technology.
A circuit of this generic type for splitting and joining radio-frequency powers has been disclosed, for example, in the prospectus Kathrein-Werke KG “Base Station Antennas for Mobile Communication, catalog 03.99”.
The circuit is arranged, for example, in an elongated housing. At one of the end faces the so-called sum port (input) can be provided. On the opposite end, for example, a first individual port can be provided. A second individual port can be provided on a transverse face, adjacent to this end face, but at right angles to it.
The power is split by means of different resistances at the individual port (different individual port resistances connected in parallel). The first individual port in this case remains unchanged (i.e., is not transformed). The second individual port is subjected, for example, to λ/4 transformation. In other words, the power split according to the prior art is provided by means of a different impedance Z (“λ/4 transformation”). The power division in this case produces a reaction on the input, however. In particular, if the division ratios differ, they cannot be set such that they are variable, so that different types and appliances must be provided for the different power division ratios.
Another circuit for splitting or joining radio-frequency power is known from U.S. Pat. No. 3,324,421. There, a main line is connected between an input port and first output port, and a branch line branches off from the main line at a branching point. An adjustable output element is provided in this circuit, which determines the magnitude of the power tapped off by varying the capacitance of a capacitor which is connected in the branch line. Depending on the measurement frequency, the output element can in this way be adapted over a narrow bandwidth, but only the measurement branch is adapted. This output element causes reactions on the impedance of the main line, however, especially at relatively high frequencies,
It is known from U.S. Pat. No. 2,657,362 for, for example, to match the impedance of an antenna to a different impedance by means of a mechanically varied combination of inductances and capacitances.
A circuit of this generic type for power splitting has also been disclosed, for example, in U.S. Pat. No. 2,667,619. This circuit comprises a main line which is connected between an input port and a first output port, and a branch line which branches off from the main line at a branching point and leads to a second output door. Furthermore, a spur line is provided, which is coupled to the branch line. According to this prior publication, serial capacitances with an electrically effective length of λ/4 or λ/2 based on the operating frequency are provided in the outputs. A movable trimming element is provided, which, via an operating element, can at the same time be moved into the main path and the branching path, engaging in its longitudinal direction. This means that the function of the distributor is provided by the simultaneous increase and decrease in the series capacitances. Since the series capacitances are a function of the wavelength, the distributor is suitable, by virtue of its design, only for channel-selective or narrowband applications. It is not possible to use this prior publication to produce a power distributor for wide bandwidths from, for example, 800 to 2200 MHz.
In this design according to the abovementioned arrangement, it is furthermore provided for one output to be interrupted by a series capacitance. Furthermore, the trimming element and the spur line are conductively connected to the inner conductors of the main line and branch line.
A largely similar circuit is also disclosed in U.S. Pat. No. 2,605,357. In contrast to the publication U.S. Pat. No. 2,667,619 mentioned above, the series capacitance is not varied by longitudinal movement of the inner conductors, but by twisting the coupling surfaces. In this case as well, the lengths of the coupling points are predetermined by the operating frequency. Thus, in this case as well, broadband use over a multiple of the wavelength is not feasible.
Thus, against the background of the generic prior art, it would be desirable to provide an improved circuit for power splitting, and in particular, an improved variable circuit for splitting or joining radio-frequency powers.
The circuit arrangement according to an exemplary non-limiting implementation is not only novel but, in terms of its overall structure and with regard to the advantages which can be achieved by it, is highly surprising. This is because one preferred embodiment of the circuit arrangement makes it possible to achieve a variable power split without the input impedance varying in the process. According to an exemplary non-limiting implementation, this is achieved by a combination of variable coupling capacitances and a variable spur line, in which case both elements can be varied in a preferred manner by means of a common control element.
The power split is in this case preferably implemented such that a further line, which is capacitively coupled, branches off from a continuous RF line at a defined point. In this case, a transformation is carried out for the resistance matching at the input port or sum port, without this having—as mentioned—any consequential effect on, or causing any change to, the input impedance. Frequency compensation or frequency predistortion is carried out on the output branch. According to an exemplary non-limiting implementation, the power split can now be varied by moving, without any problems, an adjustment or movement element which is provided, to be precise without any reaction on the input impedance. Now, according to an exemplary non-limiting implementation, not only different type appliances but only one type, which is adjustable differently, can be used for different power division ratios.
The circuit arrangement according to an exemplary non-limiting implementation can thus be installed for the most different forms of power branches in an RF broadband network, for example in the case of signal transmission in a building, for the various power branches in the individual stories, building complexes, etc. In this case, the desired power split can be set without any problems just by rotating an adjustment element such that it corresponds to the power branch to be provided.
Furthermore, a large number of distribution panels are normally required for the wiring in a building, in order to split the signals that are fed in (for example in the cellar) between a large number of lines. Sometimes it may be desirable to carry out a power split between different branch lines, possibly all having different proportions of the power, in the individual stories of a building. The advantages according to technology disclosed herein become even clearer. This is because, according to an exemplary non-limiting implementation, only a single circuit device is needed for, in particular, continuously variable power splitting, which can in each case be set without any problems for the particular requirements. This makes it possible, without any problems, to compensate for different cable lengths, cable attenuations, etc.
The power split according to an exemplary non-limiting implementation is preferably carried out using a compensating element which is arranged in a variable position. Varying the position varies the output of power into the branching line and, in the process according to an exemplary non-limiting implementation, at the same time compensates for the resistance change caused by the output variation. The compensating element, whose position can be varied mechanically, may be electrically conductive, but need not be. For example, it is just as possible to use a dielectric compensating element.
In one particularly preferred embodiment of an exemplary non-limiting implementation, the adjustment element may in this case be arranged in an axial extension for the branching line, with the main line, which runs between the input port and the further output port (that is to say between the sum port and the further individual port) being arranged transversely with respect to it.
The desired varied output can preferably be achieved by means of a mechanically adjustable probe, whose axial position can be varied, for example, by radial twisting.
However, by way of example, the compensating element may also be adjusted differently by means of some other type of adjustment mechanism. For this purpose, a further preferred exemplary embodiment provides for the control element to have the capability to be moved linearly on the circuit housing. The adjustment movement is in this case preferably carried out in the axial longitudinal direction of the circuit housing. The adjustment movement (preferably the linear adjustment movement of the compensating element) can be produced and implemented via this adjustment movement. Preferably this is internally in the adjustment element, with the adjustment movement of the compensating element being at right angles to the adjustment movement of the control element. The overall exemplary non-limiting arrangement has the further advantage that, for example, an easily visible scale can be fitted, in which case it is possible to read the current power split setting exactly, as a function of the movement position of the adjustment element.
Finally, the step-up ratio between the control element and the compensating element may also be produced non-linearly, if this is desired. Otherwise, a linear step-up ratio can be achieved at any time.
The bandwidth of the output unit may be very wide, for example 45%.
The circuit arrangement according to an exemplary non-limiting implementation may be designed to be coaxial. However, it may also be implemented by means of discrete components, or using board technology.
It should be noted, merely for the sake of completeness, that the circuit according to an exemplary non-limiting implementation may also have a number of variable output elements in order to form an n-tuple distribution panel.
In more detail, the circuit according to an exemplary non-limiting implementation for splitting or for joining radio-frequency powers, has a main line or main path (7) which is connected between an input port (1) and a first output port (3), and has a branch line (11) which branches off from the main line at a branching point (9) and leads to a second output port (5). It is preferably distinguished in that a compensating element (61) is provided which is, in particular, adjustable, or can be installed and removed differently. The compensating element can be varied by varying the capacitance of at least one capacitor (C2, C3), which is connected in the branch line (11), and/or by varying the electrical length of a spur line (37) which is coupled to the branch line (11), such that the variable magnitude of the power being tapped off at the same time also makes it possible to compensate for the resistance change caused by the change in the power split.